Mucolipidosis type IV (MLIV) is an autosomal recessive disorder typically characterized by severe psychomotor delay evident by the end of the first year of life and slowly progressive visual impairment during the first decade as a result of a combination of corneal clouding and retinal degeneration. We will evaluate the natural history of the disease yearly in up to 10 MLIV patients over 5 years. We hypothesize that over the period of observation there will be a small decline in neurological function and structure in patients with MLIV. The main outcome measures in this study will be the neurocognitive characteristics of patients with MLIV and the structural brain characteristics of patients with MLIV and in particular brain volume and diffusion tensor imaging. The evaluative tools in this study will include MRI, age appropriate measures of neurocognitive function, EEG, swallow studies, physical therapy and nutrition.